Kinetic simulations of a direct-current positivecolumn Ar plasma revealed that electron fluxes are sensitive to energy dependence of an elastic collision cross section. Paradoxical behavior of the electron flux in a coordinate-energy phase space is presented. The direction of the electron flux at the "elastic" energy region (5-10 eV) in whole volume, except the region near the wall, turned out to be oppositely directed to that conventionally assumed.Index Terms-Electron kinetic, plasma physics. I N VARIABLES of coordinate r and total electron energy ε, the Boltzmann kinetic equation for electrons represents an equation of 2-D diffusion with coefficients D r = vλ/3 and D E = (eE) 2 D r and the "velocity" of energy loss in elastic collisions V ε = δνw (see, for details, [1]-[3]), i.e.,The left-hand side of (1) is the divergence of differential electron flows [1]-[3] with respect to energy and coordinate, i.e.,Recall that electron spatial flows redistribute particles and energy in the plasma volume and form a plasma density profile [1]-[3]. These electron energy distribution function (EEDF) forming flows bear information about the fine characteristics of the discharge, such as generation and loss of charges, components and mechanisms of the electron energy balance, etc. In the local approximation (LA), when spatial term Φ r in (2) is ignored, the EEDF depends on local values of parameters at a given space point. Small corrections to the local energy distribution function, which are proportional to small gradients of the respective parameters, show up in the formation of particle Manuscript and energy fluxes, which are proportional to these gradients. In this approximation, in compliance with the fluid model in the classical transport theory, the direction of differential diffusion fluxes (i.e., the contribution of different parts of the EEDF to the total particle and energy fluxes) coincides with the directions of the total fluxes. Once the plasma becomes more inhomogeneous and the particle and energy fluxes start growing, these fluxes separate out and become more independent of each other. The radial flows of electrons may behave in surprisingly differing manners in various domains of the phase space, and the concept of differential fluxes Φ(ε) turns out to be an efficient tool in gaining a deeper insight into the physics of spatial mechanisms underlying the EEDF formation [1]- [3]. As it was pointed in [1]-[3], when the electron flux on phase plane (ε, r) is directed strictly up along the energy axis, the EEDF is local; when they are shifted along the coordinate, the LA cannot be applied, and the EEDF is nonlocal. This paper shows that the situation is more complicated. The reason is that analyses in [1]-[3] were performed for inelastic electron energy balance, wherein term V ε in (2) can be omitted. However, at moderate and high pressures, the electron energy balance is elastic, wherein energy flux Γ ε represents the difference of two large value terms, each of them larger than Φ r . This is why, on the one hand,...
